Carbon is a commercially essential element which in elemental form is a material both found in nature (e.g., coal) and is also made from industrial processes. Methods of making carbon are essential to traditional and advanced technology industries. Elemental carbon can be found in various forms and allotropes including, for example, amorphous carbon, crystalline carbon, carbon black, graphite, and diamond. Other forms of carbon include, for example, glassy carbon, diamond like carbon, carbene, and carbyne. Nature also provides different forms of coal which is largely carbon. Carbon powder and carbon fibers are other forms of carbon essential to industry.
Nanoscale forms of carbon are also known including fullerenes (including C60 and C70 fullerenes), carbon nanotubes (both single walled and multi-walled), graphene (single layered or multi-layered), and aerogels. Diamond can be made synthetically by high pressure/high temperature routes or by physical or chemical vapor deposition routes. Vapor deposition can produce microcrystalline or nanocrystalline diamond in thin film form. Nanoscale forms of carbon represent a critical aspect of newer and better devices ranging from the next generation of miniaturized transistors to more efficient batteries. Large area forms of nanoscale forms of carbon such as thin diamond films and graphene are also critical.
In general, carbon production is associated with arduous process conditions such as high temperature, high pressure, vacuum, and/or high energy sources like plasma. Such conditions generate expense and are energy-intensive. They also generally lack versatility (e.g., inability for a single process to be altered to produce different allotropes of carbon, or different size scales of carbon).
For example, DE 1667532 Greiner (1971) describes what is said to be low temperature diamond production from an electrochemical system which can include use of carbide in the electrolyte with use of temperatures of 600° C. to 1000° C. However, no data are provided.
Also, U.S. Pat. No. 4,738,759 (1988) describes an electrolysis process wherein calcium carbide can be subjected to electrolysis to form graphite sponge at the anode. Temperatures are used such as 700° C. to 1,000° C.
A Chen M. S. thesis, August 2002, Univ. N. Texas, describes electrochemical deposition of films of amorphous carbon and diamond like carbon (DLC). Electrochemical deposition was carried out using a low temperature (less than −40° C.) solution of acetylene in liquid ammonia.
Kulak, Electrochem. Comm., 5, 2003, 301-305 describes room temperature electrodeposition of very thin, porous film containing carbon (50-100 nm thick) from a solution of lithium acetylide. However, the microscopic images of the film indicate a low quality material (FIG. 2) and much of the film is not carbon apparently.
US 2011/0290655 (Nishikiori; Toyota) describes a method for electrochemically depositing carbon film on an anode substrate using a molten salt electrolyte bath comprising a carbide ion and applying a DC voltage to deposit the carbon film. The bath temperature is 250° C. to 800° C. The carbon film is said to be mainly amorphous carbon including graphite-like carbon according to x-ray diffraction.
Despite such advances, a need exists for better, commercially friendly, and environmentally friendly approaches to elemental carbon material production. This includes elemental carbon material that has high elemental purity and also a commercially useful structure and morphology. One also wants to be able to control the form and morphology of the elemental carbon material. Inexpensive methods are also needed.